The dealers in rubber stamp maker’s supplies sell special steel moulds for the purpose of making them. This does away with all necessity for making matrices, and making up a flask, etc. The general manipulation is that given above. Where many are to be made the regular mould is by all means to be recommended.
Sometimes type are made by cementing single letters made by the stamp process upon wooden bodies.
CHAPTER VII.
THE MAKING OF STAMPS AND TYPE FROM VULCANIZED INDIA RUBBER.
Although all reference hitherto in the matters of stamps and type has been to their manufacture from uncured india rubber, a good deal can be done with vulcanized and cured gum. The stock that is known in the trade as pure gum, such as is used for bicycle tyres, for steam packing and the like, can be made to yield to moulding to a certain degree. It will not flow and unite as will the uncured gum, but it is evident that in certain cases its stiffness is even an advantage. Thus with it, rubber type can be made without any flask or frame. The material has stiffness enough to support itself.
The manipulation is of the simplest. A piece is cut out with a knife so as to be of proper thickness and size. It should be a little thicker than will ultimately be required. The two opposite surfaces should be smooth and parallel. It is talced, and placed in the press with the matrix beneath it, and subjected to pressure by the screws being turned down. It is then placed in the vulcanizing chamber and heated to about 284° F. (140° C.). After it has become hot it softens a little. The press is removed from the hot chamber and is again screwed down as hard as the matrix can stand. This point is largely a matter of judgment. The heat is largely indifferent as long as it is anywhere near the above temperature.
By one or two repetitions of the pressing and heating the softened india rubber can be made to take quite a deep impression from a suitable matrix. It is allowed to cool under full pressure. When removed from the press, it will retain the characters.
It is evident that impressions in as high relief or as deep and clear as those yielded by uncured india rubber need not be expected. But where the other cannot be had, or where some experimental or temporary work only is on hand, this process will be very convenient.
The material may be half an inch thick. From such india rubber type can be cut with advantage.
Old rubber can be thus used. The writer has obtained excellent results from pieces of an old discarded bicycle tyre.